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e85 a/f ratio

EFI Tuning Fundamentals

Discussion and questions related to the course EFI Tuning Fundamentals


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Just going to give you guys a situation. I have an evo 8 that is tuned on e85. Now based off the PDF file attached for perfect ratios,it says it should be 9.8. Now in my opinion (correct me if im wrong) when im sitting there idling in neutral,shouldnt it be 9.8 (perfect)? I have an a/f ratio gauge and its always reading around 15.0 during idle. Tuner said e85 is meant to run leaner and that's how the power gain is achieved. Is that all wrong?

Does your car run only e85, or does it have an ethanol sensor to allow you to use E10/E0 (ie, normal gasoline)?

The reason for asking, is that Wideband AFR gauges actually detect oxygen, and need to be configured to provide the AFR depending on fuel. What they really detect is the ratio of oxygen to ideal oxygen for a stoichiometric combustion (the 9.8 AFR for E85 or 14.7 AFR for a typical E0 fuel). So if your AFR is set for Gasoline, it should read close to 14.7 AFR even if you are using E85 that is really 9.8. Think of it as 14.7 Gasoline AFR. For cars tuned for flex fuel, typically folks working in AFR tend to use Gasoline AFR regardless of the ethanol content.

However, many tuners prefer to work in units of Lambda -- one reason is because Lambda 1.0 is the same regardless of the fuel used, and if your Wideband gauge can be set to Lambda, then you will find it will read close to 1.0 at idle (and maybe cruise) regardless of the ethanol content in your fuel (assuming an enthanol sensor and a flex-fuel tune).

No,its full e85. Do you have any idea if an AEM wideband could be switched?

It depends on which Gauge you have. AEM makes several models:

https://www.aemelectronics.com/products/wideband-uego-air-fuel-controllers

Looking at 30-4100, it has a switch that allows display of Gasoline AFR or Lambda (it has a replaceable face for Lambda readings, too)

30-5130 (analog style) is for Gasoline AFR but 30-5143 is for e85 AFR.

Those are just a couple that I looked at, you can get the instructions for each product by scrolling down on the pages until you see the price/purchase button. There is usually an instructions button located there too.

I would suggest you figure out which model you have then contact AEM and see if your gauge can be updated or configured for e85 use.